1. Field of the Invention
The invention relates to the field of medical electronics and, more particularly, has as its object a system for wireless transmission of medical data.
2. Discussion of the Background
Certain medical examinations use the detection of electrical fields. This is particularly the case in electrocardiography.
Conventionally, to perform an electrocardiogram, electrodes are placed at precise points of the body and the voltages detected between these points are amplified in a differential amplifier with suitable characteristics, followed by a graphic recorder. In units used for monitoring, the graphic recorder is replaced or completed by an oscilloscope. The diagnostic value of the electrocardiogram or "EKG" is considerable: changes of the waveforms recorded are very significant.
Conventionally, for complete examinations intended to characterize completely the electric activity of the heart in 3 dimensions, 3 characterization signals are formed from 10 electrodes: 3 electrodes called "principal," D, G, P; 1 reference electrode; and 6 electrodes called "precordial." The patients are lying down and wires connect the electrodes placed on the body to the electronic circuits of the electrocardiograph. This connection is, for example, performed as follows: 10 elemental leads are connected to 10 electrodes placed at the points required for the examination. These 10 leads are connected to a concentrator by "banana"-type connectors and a multiconductor shielded cable connects the concentrator to the recorder via a DIN connector. This structure is heavy, expensive, constraining for the patient and its safety of operation is not even completely assured since breaks or anomalies in the wire connections, particularly when the central core of a lead is damaged, produce noise and artifacts, even a disappearance of the corresponding signal.
Moreover, if the lying down position is suitable for some measurements, it is not suitable for measurements during stress tests. Now these examinations are very advantageous in following the variations of the EKG signals as a function of stress. In the standard systems, the patient is a "home trainer" and the problems of vibration, of sudation accentuate the deficiencies of the leads. In addition, the equipment, which is in the way, carried by the patient restricts him during his effort.
Other pieces of equipment, of a portable type, are provided to record the EKG signals on a magnetic tape recorder carried on the belt and connected by leads to the electrodes. Such pieces of equipment that can be used on the outside for monitoring patients throughout their activity can make it possible to record all the signals for 12H or 24H to find anomalies, connected with the activity, that are undetectable during office examinations. Such a piece of equipment does not make possible a monitoring of the patient in real time but only in delayed time after reading, optionally speeded up, of the tape.
A piece of test equipment is also known that is particularly intended for athletes in particular to improve their training. This piece of equipment comprises a transmitter placed on the chest of the athlete which detects the overshootings in relation to a threshold ("R" points of the EKG PQRST complex signal), and wirelessly transmits pulses corresponding to these points to a receiving microcomputer carried on the wrist. This wireless transmission is performed according to the principle of the magnetic field; water, clothes or the wet body do not disturb the transmission. The piece of equipment makes it possible to record the cardiac frequency according to a sampling at a pace of 5, 15 or 60 sec, for example for a total period that is a function of the storage capacities.
As the short description given above shows, this equipment makes it possible to follow only the cardiac frequency, and the use of the results can be realized in real time only by the athlete and only to the extent that a display can be provided on the receiver. As in the piece of equipment described previously, such a piece of equipment does not permit real-time following by a medical team.